The present invention pertains to polymers prepared from a solid inorganic oxide (e.g., silica) supported transition metal catalysts.
The polymerization of ethylene and the copolymerization of ethylene with other olefins is known to be carried out by gas phase, solution and/or suspension (slurry) polymerization processes. Advantages of the solution process include short reaction times, improved heat removal and monomer conversion for mass and energy control of polymerizations and single-phase reaction environments for controlling reaction dynamics. A most advantageous solution polymerization would be conducted at even higher reaction temperatures yet with a polymerization catalyst that yields sufficiently high molecular weight polymers with a high catalyst efficiency at these higher temperatures which lowers catalyst residues in the product and/or permits complete omission of the catalyst removal step.
In the suspension (slurry) polymerization of olefins, the advantages are low pressures, low temperatures and the ability to make very high molecular weight polymers. It is advantageous to carry out these reactions with sufficiently high polymerization efficiencies such that residues from the polymerization catalyst do not have to be removed from the resulting polymer.
There are many polymerization catalysts for suspension polymerization known in the art. Hagerty et al. in U.S. Pat. No. 4,562,169 disclose the preparation of a supported catalyst by treating a solid porous carrier having reactive OH groups such as silica in a liquid medium with an organomagnesium compound to react with the OH groups on the carrier; evaporating said liquid to precipitate magnesium onto the carrier and recovering a supported magnesium composition in the form of a dry, free-flowing powder; reacting the powder with a tetravalent titanium compound in a liquid medium. The catalyst is useful in the polymerization of olefins.
Nowlin in U.S. Pat. No. 4,593,009 and U.S. Pat. No. 4,672,096 discloses a catalyst for polymerizing olefins which catalyst is prepared by treating a carrier containing OH groups with an organomagnesium composition and contacting the thus-formed magnesium-containing carrier with a solution of at least one tetravalent vanadium compound or a solution containing both a vanadium compound and a titanium compound.
Gessel in U.S. Pat. No. 4,244,838 describes catalysts prepared from an organomagnesium compound, an organic hydroxyl-containing material and a transition metal halide. These solids produced by this reaction are isolated and washed prior to use in a polymerization.
Fuentes et al. in U.S. Pat. No. 4,544,647 disclose catalyst compositions prepared from an organomagnesium material, an organic hydroxyl-containing material, a reducing halide source and a transition metal compound.
Marchand et al. in U.S. Pat. No. 4,910,272 describe a process for polymerizing olefins in the presence of a catalyst prepared from an inorganic oxide, an organomagnesium material, an organic hydroxyl-containing material, a reducing halide source and a transition metal compound.
The catalyst efficiency of these catalysts is, in general, decreased with increased polymerization temperatures, specifically temperatures above 140xc2x0 C.
The catalysts known for solution polymerization comprise an organomagnesium component, an aluminum halide and/or an additional halide source and a transition metal compound. Lowery et al in U.S. Pat. No. 4,250,288 describes such compositions that are useful in the polymerization of xcex1-olefins above 140xc2x0 C.
Sakurai et al. in U.S. Pat. No. 4,330,646 describes similar catalysts containing a titanium or a titanium and/or a vanadium compound as the transition metal component. These catalysts are useful at polymerization temperatures of at least 180xc2x0 C. The disadvantage of these catalysts is that the reactions that produce the catalyst solids are highly exothermic and difficult to control and reproduce. These catalyst compositions also contain a large excess of halide with respect to the transition metal component and yield polymers with a relatively high halide content. The composition as a whole is used directly in the polymerization of olefins.
It is well known in the art to optimize the properties of linear low density polyethylene (LLDPE) by variation in product molecular weight, molecular weight distribution (MWD) and density to match the required product application. Increasing the molecular weight, narrowing the MWD or lowering the density of LLDPE usually results in improved impact strength and puncture resistance properties. Molecular weight of the polymer prepared in Ziegler Natta catalyzed processes (as described by Professor Karl Ziegler in U.S. Pat. Nos. Numbers 3,113,115 and 3,257,332) is typically controlled in the process by the addition of varying amounts of telogens most commonly hydrogen. Similarly the density of the product is typically controlled by varying the comonomer concentration in the reaction medium.
In addition to optimizing product molecular weight and density for a given product application further improvement in resin performance can be obtained by narrowing the molecular weight distribution of a given melt index and density product. U.S. Pat. No. 4,612,300 describes a process for preparing LLDPE copolymers with narrow molecular weight distribution using a specific catalyst formulation, resulting in polymers for film applications with improved clarity and toughness.
Yet another property known to improve the clarity and toughness of alpha-olefin polymers is a small spherulite size as described for polypropylene (Kuhre et al., SPE Journal, October, 1964, pps 1113-1119) and polyethylene (Narh et al, J. Mat. Sci, 15 (1980), pps 2001-2009). Similarly, U.S. Pat. No 4,205,021 discloses copolymers with densities from 0.90 to 0.94 g/cm3 with exceedingly high weight average molecular weight but with the intrinsic viscosities of conventional ethylene copolymers and spherulite sizes of not more than six microns.
Linear low density polyethylene (LLDPE) produced with Ziegler catalysts have side groups introduced into the molecule from copolymerization with comonomers. In the case of 1-octene this side group would have six carbons atoms i.e. a hexyl chain. The distribution of these side groups or branches along and among all the polymer molecules is known as the polymer Short Chain Branching Distribution (SCBD) and the nature of this distribution has a strong impact on product properties and performance.
U.S. Pat. No. 4,438,238 discloses ethylene/alpha olefin copolymers with improved properties formed by mixing copolymers of high molecular weight and specified SCB (short chain branches/1000 carbons) with copolymers of lower molecular weight and specified SCB results in resins of 0.91 to 0.94 g/cm3 density and melt index of 0.02 to 50 g/10 min and melt flow ratio of 35 to 250 with excellent strength properties.
U.S. Pat. No. 4,918,038 discloses a process for the production of ethylene homopolymers or copolymers with a broad and/or bimodal molecular weight distribution using a mixed catalyst system. One advantage of this system is that the product can be made in a single reactor rather than using multistage reactors which raise questions of efficiency and cost.
U.S. Pat. No. 4,481,342 teaches a method of preparing an ethylene/alpha olefin copolymer of varying alpha olefin content, the incorporation of which is controlled by the porosity and pore radius of the magnesium chloride support.
U.S. Pat. No. 4,522,987 discloses a process using a chromium based catalyst system in which the incorporation of comonomer into the polymer chain occurs in a xe2x80x9csuper-randomxe2x80x9d fashion as described by the relative comonomer dispersity (RMD) as determined by N.M.R. The dispersity is controlled by the nature of the comonomer and varying its concentration in mole percent in the gas phase.
U.S. Pat. No. 3,645,992 discloses a continuous process for the preparation of homogeneous random partly crystalline copolymers of narrow MWD. The degree of homogeneity is controlled by varying the reactor temperature. Similarly homogeneity was decreased when R2AlCl was used as cocatalyst rather than R1.5 AlCl1.5 or RAlCl2. Similarly increasing the ratio of cocatalyst to catalyst to greater than 9:1 for octene copolymers was required to yield homogeneous copolymers.
It would be desirable to have available catalyst compositions which exhibit significantly higher polymerization efficiencies based on the transition metal and the halide. It would also be desirable to have available catalyst compositions which exhibit these high efficiencies while being prepared in a manner which did not require the isolation and/or washing of the solid catalytic product. It would be further desirable to ease the process of preparation of the catalyst in order to increase reproducibility and quality of the catalyst.
It would also be desirable to have available such catalysts which would provide polymers having a high molecular weight and a relatively narrow molecular weight distribution and which exhibit more tolerance to hydrogen at polymerization temperatures of at least 180xc2x0 C. and even greater than 200xc2x0 C.
Also, it would be advantageous to have a solution process which, at a given melt index and density, results in a narrow molecular weight distribution product with small spherulite size, the SCBD of which, can be easily controlled to yield the desired combination of polymer properties for the specific product application.
One aspect of the present invention pertains to a supported transition metal catalyst component which comprises an inert liquid medium having slurried therein a composition comprising the product resulting from contacting (1) a porous solid inorganic oxide support material selected from the group consisting of silica, alumina, or a combination of silica and alumina, said support material containing not greater than about 5 millimoles of hydroxyl groups per gram of support material and a particle size not greater than about 10 microns and a surface area of from about 50 to about 800 m2/g; (2) a hydrocarbon soluble organomagnesium alkoxide or hydrocarbon soluble magnesium dialkoxide; (3) a titanium compound; optionally (4) a vanadium compound; and (5) a Group IIIA metal alkyl halide; and wherein the components are employed in amounts which provide the following atomic ratios:
Si+Al (from the inorganic oxide support):Mg of from about 1:1 to about 30:1;
Mg:Ti of from about 0.2:1 to about 10:1;
Mg:V of from about 0:1 to about 10:1;
Mg:IIIA metal of from about 0.05:1 to about 5:1; and
V:Ti of from about 0:1 to about 5:1.
Another aspect of the present invention pertains to a process for preparing a supported transition metal catalyst component slurried in an inert liquid medium, which process comprises (A) forming in an inert atmosphere which excludes oxygen and moisture a slurry of (1) a porous inorganic oxide support material selected from the group consisting of silica, alumina, or a combination of silica and alumina, said support material containing not greater than about 5 millimoles of hydroxyl groups per gram of support material and a particle size not greater than about 10 microns and a surface area of from about 50 to about 800 m2/g in an inert organic liquid medium; (B) mixing said slurry with (2) a hydrocarbon soluble organomagnesium alkoxide or hydrocarbon soluble magnesium dialkoxide and stirring the resulting mixture at a temperature of from about xe2x88x9220xc2x0 C. to about 120xc2x0 C. for a time sufficient to saturate the surface of the support material; (C) mixing the product from (B) with (3) a titanium compound or a combination of a titanium compound and (4) a vanadium compound or adding the titanium compound and vanadium compound separately and stirring the resultant mixture at a temperature of from about xe2x88x9220xc2x0 C. to about 120xc2x0 C. for a time sufficient to allow complete reaction of the titanium compound and the vanadium compound with the organomagnesium moieties remaining on the solid support; (D) mixing the product from (C) with an inert organic solution of (5) a Group IIIA metal alkyl halide at a temperature of from about xe2x88x9220xc2x0 C. to about 120xc2x0 C. for a time sufficient to complete the reduction of the titanium and vanadium, if present, compounds to their final oxidation state.
A further aspect of the present invention pertains to a process for polymerizing one or more xcex1-olefins and optionally one or more polymerizable ethylenically unsaturated compounds other than an xcex1-olefin which process comprises contacting the materials to be polymerized with (A) a supported transition metal containing catalyst component comprising the product resulting from contacting (1) a porous inorganic oxide support material selected from the group consisting of silica, alumina, or a combination of silica and alumina, said support material containing not greater than about 5 millimoles of hydroxyl groups per gram of support material and a particle size less than 10 microns and a surface area of from about 50 to about 800 m2/g; (2) a hydrocarbon soluble organomagnesium alkoxide or hydrocarbon soluble magnesium dialkoxide; (3) a titanium compound; optionally (4) a vanadium compound; and (5) a Group IIIA metal alkyl halide; and wherein the components are employed in amounts which provide the following atomic ratios:
Si+Al:Mg of from about 1:1 to about 30:1;
Mg:Ti of from about 0.2:1 to about 10:1;
Mg:V of from about 0.2:1 to about 10:1;
Mg:IIIA metal of from about 0.05:1 to about 5:1;
V:Ti of from about 0:1 to about 5:1; and
(B) a cocatalyst or activator for component (A).
Still another object of the present invention pertains to process for varying the short chain branching distribution (SCBD) of ethylene/xcex1-olefin copolymers which comprises (I) subjecting ethylene and one or more xcex1-olefin comonomers to solution polymerization conditions in the presence of a catalyst composition comprising (A) a supported transition metal containing catalyst component comprising the product resulting from contacting (1) a porous inorganic oxide support material selected from the group consisting of silica, alumina, or a combination of silica and alumina, said support material containing not greater than about 5 millimoles of hydroxyl groups per gram of support material and a particle size less than 10 microns and a surface area of from about 50 to about 800 m2/g; (2) a hydrocarbon soluble organomagnesium alkoxide or hydrocarbon soluble magnesium dialkoxide; (3) a titanium compound; optionally (4) a vanadium compound; and (5) a Group IIIA metal alkyl halide; and wherein the components are employed in amounts which provide the following atomic ratios:
Si+Al:Mg of from about 1:1 to about 30:1;
Mg:Ti of from about 0.2:1 to about 10:1;
Mg:V of from about 0.2:1 to about 10:1;
Mg:IIIA metal of from about 0.05:1 to about 5:1;
V:Ti of from about 0.8:1 to about 1.2:1; and
(B) a cocatalyst or activator for component (A); and
(II) controlling the SCBD by the ratio of Mg:Ti in component (A).
The present invention provides catalyst compositions which exhibit high polymerization efficiencies based on the transition metal and the halide and are prepared in a manner which do not require the isolation and/or washing of the solid catalytic product. The catalysts which contain vanadium produce a polymer having a high molecular weight and a relatively narrow molecular weight distribution when the polymers are prepared by the solution process.
The present invention provides catalyst compositions which exhibit high polymerization efficiencies based on the transition metal and the halide and are prepared in a manner which do not require the isolation and/or washing of the solid catalytic product. The catalysts which contain vanadium produce a polymer having a relatively broad molecular weight distribution when the polymers are prepared by the slurry process.
The present invention also provides a process for preparing ethylene/xcex1-olefin copolymers which at a given melt index and density results in a narrow molecular weight distribution product with small spherulite size and controlling the short chain branching distribution by varying the Mg:Ti atomic ratio so as to produce copolymers with a desired combination of polymer properties for specific product applications.
Yet another aspect of the present invention is to provide ethylene/xcex1-olefin copolymers which are particularly effective in making films, especially cast films used in pallet wrapping applications. The copolymers are advantageously made using the catalyst compositions and process described herein. The copolymers can be used, e.g., as a core layer in a multilayer coextruded cast film structure, or they can be used by themselves in the film. The specific copolymers have a high density fraction greater than about 17 percent and a molecular weight distribution (indicated by Mw/Mn) of less than about 3.6 and, when converted into film form, provide greater overall film stretchability and puncture resistance.
All references herein to elements or metals belonging to a certain Group refers to the Periodic Table Of The Elements published by the Sargent-Welch Scientific Company, Skokie Ill., catalog number S-18806 (1968).
The term xe2x80x9chydrocarbylxe2x80x9d as employed herein means any aliphatic, cycloaliphatic, aromatic, aryl substituted aliphatic, aryl substituted cycloaliphatic, aliphatic substituted aromatic or aliphatic substituted cycloaliphatic groups.
The term xe2x80x9chydrocarbyloxyxe2x80x9d means a hydrocarbyl group having an oxygen linkage between it and the carbon atom to which it is attached.
The term xe2x80x9ccopolymerxe2x80x9d as employed herein means a polymer produced by polymerizing a mixture of two or more polymerizable ethylenically unsaturated monomers.
The transition metal catalyst of the present invention can be prepared in the following manner.
The porous inorganic oxide support material is slurried in an inert organic diluent under conditions which exclude oxygen (air) and moisture at a temperature of from about xe2x88x9220xc2x0 C. to about 120xc2x0 C., preferably from about 0xc2x0 C. to about 100xc2x0 C., more preferably from about 20xc2x0 C. to 70xc2x0 C. No particular time is required other than that to form a uniform slurry of the support in the diluent. This depends upon the amounts involved, but usually a good uniform slurry can be formed in about 1 hour in a concentration range from about 0.1 to about 15, preferably from about 0.5 to about 10, more preferably from about 1 to about 7, weight percent.
To this slurry is then added the hydrocarbon soluble organo magnesium alkoxide or hydrocarbon soluble magnesium dialkoxide, again tinder conditions which exclude oxygen (air) and moisture, and the mixture stirred at a temperature of from xe2x88x9220xc2x0 C. to about 120xc2x0 C., preferably from about 0xc2x0 C. to about 100xc2x0 C., more preferably from about 20xc2x0 C. to about 70xc2x0 C. for a time sufficient to react the magnesium compound with surface of the solid support, usually from about 0.1 to about 10, preferably from about 0.2 to about 8, more preferably from about 0.5 to about 4 hours.
After the above addition of the magnesium compound, a titanium compound or a combination of a titanium compound and a vanadium compound s added, again under conditions which excludes oxygen (air) and moisture, and the mixture stirred at a temperature of from xe2x88x9220xc2x0 C. to about 120xc2x0 C., preferably from about 0xc2x0 C. to about 100xc2x0 C., more preferably from about 20xc2x0 C. to 70xc2x0 C. for a time sufficient to completely react the titanium compound and the vanadium compound with the reactive silica and magnesium functionalities, usually from about 0.1 to about 100, preferably from about 0.5 to about 20, more preferably from about 1 to about 10, hours. The titanium and vanadium compounds can be premixed prior to their addition or they can be added separately in any order to the product resulting from blending the magnesium compound with the slurry of the inorganic oxide support material.
Following the addition and mixing of the titanium and/or vanadium compounds, a Group IIIA metal alkyl halide is added and the mixture is stirred at a temperature of from about xe2x88x9220xc2x0 C. to about 120xc2x0 C., preferably from about 0xc2x0 C. to about 100xc2x0 C., more preferably from about 20xc2x0 C to 70xc2x0 C. for a time sufficient to reduce the titanium compound and vanadium compound, if present, to their final oxidation states, usually from about 1 to about 100, preferably from about 2 to about 50, more preferably from about 5 to about 20, hours.
Upon completion of the addition and mixing of the Group IIIA metal alkyl halide, the thus formed transition metal catalyst component can be employed in the polymerization of xcex1-olefins as is without isolation of the solid components from the liquid components. The transition metal catalyst component can be employed immediately upon its preparation or the component can be stored under inert conditions for some length of time, usually for periods of time as long as 90 days.
The components can also, if desired, be added in the order as follows: SiO2+Mg compound+Ti compound+Al compound+V compound.
The components can also, if desired, be added in the order as follows: SiO2+Mg compound+Al compound+Ti compound+V compound.
Oxygen (air) and moisture can be excluded during catalyst preparation by conducting the preparation in an inert atmosphere such as, for example, nitrogen, argon, xenon, methane and the like.
Porous Support Material
Suitable porous silica or alumina support materials which can be employed herein include, those containing is not greater than about 5, preferably not greater than about 4, more preferably not greater than about 3, millimoles of hydroxyl groups (OH) per gram of support material. These hydroxyl (OH) groups are isolated silanol groups on the silica surface.
The hydroxyl groups can be reduced or eliminated by treating the support material either thermally or chemically. Thermally, the support material can be heated at temperatures of from about 250xc2x0 C. to about 870xc2x0 C., more preferably from about 600xc2x0 C. to 800xc2x0 C. for a time sufficient to reach the equilibrium hydroxyl group concentration, usually from about 1 to about 24, preferably from about 2 to about 20, more preferably from about 3 to about 12, hours.
The hydroxyl (OH) groups can be removed or reduced chemically by treating the support material with SiCl4, chlorosilanes, silylamines, or any combination thereof and the like at a temperature of from about xe2x88x9220xc2x0 C. to about 120xc2x0 C., more preferably from about 0xc2x0 C. to 40xc2x0 C. for a time sufficient to reduce the hydroxyl content to the desired value, usually less than about 30 minutes.
The porous support material has a particle size of not greater than about 10, preferably from about 0.1 to about 10, more preferably from about 1 to about 9, most preferably from about 2 to about 8, microns and a surface area in the range of from about 50 to about 800, preferably from about 150 to about 600, more preferably from about 300 to about 500, m2/g.
The particle size of the support is important as it has been discovered that lowering the particle size of the support below 10 microns while maintaining the support surface area and porosity results in an unexpected increase in the catalyst productivity and hence a reduction in product chloride and titanium residues relative to products of the same catalyst made on a support of equivalent surface area and porosity but larger particle size.
Inert Liquid Diluent
Suitable inert liquid diluents which can be employed to slurry the inorganic oxide support material and as a diluent for any of the other components employed in the preparation of the catalyst include, for example, aliphatic hydrocarbons, aromatic hydrocarbons, naphthinic hydrocarbons, or any combination thereof and the like. Particularly suitable solvents include, for example, pentane, isopentane, hexane, heptane, octane, isooctane, nonane, isononane, decane, cyclohexane, methylcyclohexane, toluene, any combination of any two or more of such diluents, or any combination of any two or more of such diluents and the like.
Magnesium Compound
Suitable magnesium compounds which can be employed in the preparation of the transition metal catalyst component include, for example, those hydrocarbon soluble organomagnesium compounds represented by the formula RxMg(OR)y; wherein each R is independently a hydrocarbyl group having from 1 to about 20, preferably from about 1 to about 10, more preferably from about 2 to about 8, carbon atoms; x+y=2; and 0.5xe2x89xa6yxe2x89xa62. Preferably, x has a value of zero or 1 and y has a value of 1 or 2 and most preferably, x has a value of 1 and y has a value of 1.
Particularly suitable magnesium compounds include, for example, n-butylmagnesium butoxide, ethylmagnesium butoxide, butylmagnesium ethoxide, octylmagnesium ethoxide, butylmagensium i-propoxide, ethylmagnesium i-propoxide, butylmagnesium n-propoxide, ethylmagnesium n-propoxide, s-butylmagnesium butoxide, butylmagnesium 2,4-dimethylpent-3-oxide, n-butylmagnesium octoxide, s-butylmagnesium octoxide, or any combination thereof and the like.
Also suitable are the hydrocarbon soluble reaction product (dialkoxide) of a magnesium dihydrocarbyl (MgR2) compound and an oxygen-containing compound (ROH) such as, for example, an aliphatic or cycloaliphatic or acyclic C5-C18 beta or gamma alkyl-substituted secondary or tertiary monohydric alcohol, as disclosed by Kamienski in U.S. Pat. No. 4,748,283 which is incorporated by reference. The reaction is preferably conducted in the presence of a liquid hydrocarbon media. The alcohol is usually employed in slightly more than twice the molar equivalent, based on magnesium. The reaction is usually conducted at temperatures not in excess of about 50xc2x0 C., preferably below 40xc2x0 C. Particularly suitable oxygen containing compounds include, for example, 2,4-dimethyl-3-pentanol, 2,3-dimethyl-2-butanol, 2,4-dimethyl-3-hexanol, 2,6-dimethyl-4-heptanol, 2,6-dimethyl-cyclohexanol, or any combination thereof and the like. Particularly suitable magnesium dialkyl compounds include, for example, butylethylmagnesium, dibutylmagnesium, dihexylmagnesium, butyloctylmagnesium, any combination thereof and the like.
Titanium Compound
Suitable titanium compounds which can be employed in the preparation of the transition metal catalyst component include, for example, those represented by the formula TiX4xe2x88x92a(ORxe2x80x2)a; wherein each Rxe2x80x2 is independently an alkyl group having from 1 to about 20, preferably from about 1 to about 10, more preferably from about 2 to about 8, carbon atoms; X is a halogen atom, preferably chlorine; and a has a value from zero to 4. Particularly suitable titanium compounds include, for example, titanium tetrachloride (TiCl4), titanium tetraisopropoxide (Ti(O-i-C3H7)4), titanium tetraethoxide (Ti(OC2H5)4), titanium tetrabutoxide (Ti(OC4H9)4), titanium triisopropoxidechloride (Ti(O-i-C3H7)3Cl), or any combination thereof and the like.
Vanadium Compound
In the solution process, when it is desirable to produce xcex1-olefin polymers which have a high molecular weight and a relatively narrower molecular weight distribution than that produced with the catalyst containing only titanium as the transition metal, a vanadium compound can be added as a portion of the transition metal component during preparation of the catalyst. A narrowing of the molecular weight distribution is indicated by a lowering of the I10/I2 value of the polymer.
By the term xe2x80x9crelatively narrow molecular weight distributionxe2x80x9d it is meant that the resulting polymer produced in the presence of a catalyst containing both titanium and vanadium has a narrower molecular weight distribution than the polymer produced under similar conditions with a similar catalyst prepared without the vanadium component.
In the slurry process when it is desirable to produce xcex1-olefin polymers which have a high molecular weight and a relatively broad molecular weight distribution than that produced with the catalyst containing only titanium as the transition metal, a vanadium compound can be added as a portion of the transition metal component during preparation of the catalyst. A broadening of the molecular weight distribution is indicated by an increase of the I20/I2, high load melt flow ratio (HLMFR), value of the polymer.
By the term xe2x80x9crelatively broad molecular weight distributionxe2x80x9d it is meant that the resulting polymer produced in the presence of a catalyst containing both titanium and vanadium has a broader molecular weight distribution than the polymer produced under similar conditions with a similar catalyst prepared without the vanadium component.
Suitable vanadium compounds which can be employed in the preparation of the transition metal catalyst include, for example, those represented by the formulas VX4 and V(O)X3; wherein each X is independently OR or a halogen atom, preferably chlorine; each R is independently an alkyl group having from 1 to about 20, preferably from about 2 to about 8, more preferably from about 2 to about 4, carbon atoms. Particularly suitable vanadium compounds include, for example, vanadium tetrachloride (VCl4), vanadium trichloride oxide (V(O)Cl3), vanadium triisopropoxide oxide (V(O)(Oxe2x80x94ixe2x80x94C3H7)3), vanadium triethoxide oxide (V(O)(OC2H5)3), any combination thereof and the like.
Organo Halide Compounds of a Group IIIA Metal
Suitable organo halide compounds of a group IIIA Metal which can be employed in the preparation of the transition metal catalyst include, for example, those represented by the formula Rxe2x80x2yMXz; wherein M is a metal from Group IIIA of the Periodic Table of the Elements, preferably aluminum or boron; each Rxe2x80x2 is independently an alkyl group having from 1 to about 20, preferably from about 1 to about 10, more preferably from about 2 to about 8, carbon atoms; X is a halogen atom, preferably chlorine; y and z each independently have a value from 1 to a value equal to the valence of M minus 1 and y+z has a value equal to the valence of M. Particularly suitable such organo halide compounds include, for example, ethylaluminum dichloride, ethylaluminum sesquichloride, diethylaluminum chloride, isobutylaluminum dichloride, diisobutylaluminum chloride, octylaluminum dichloride, any combination thereof and the like.
Component Amounts
For use in the solution process, the components are employed in quantities which provide an atomic ratio as follows:
Si and/or Al(from the inorganic oxide support):Mg of from about 1:1 to about 50:1, preferably from about 2:1 to about 40:1, more preferably from about 4:1 to about 20:1;
Mg:group IIIA metal of from about 0.01:1 to about 100:1, preferably from about 0.05:1 to about 10:1, more preferably from about 0.1:1 to about 5:1.
Mg:Ti of from about 0.05:1 to about 40:1, preferably from about 0.1:1 to about 20:1, more preferably from about 0.2:1 to about 10:1;
Mg:V, when V is present, of from about 0.05:1 to about 40:1, preferably from about 0.1:1 to about 20:1, more preferably from about 0.2:1 to about 10:1;
V:Ti of from about 0:1 to about 20:1, preferably from about 0.1:1 to about 10:1, more preferably from about 0.2:1 to about 5:1.
However, when it is desired to employ the solution process to vary the short chain branching distribution (SCBD) of ethylene/xcex1-olefin copolymers, the V:Ti atomic ratio is from about 0.8:1 to about 1.2:1, preferably about 1:1. For making the copolymers useful for making films of the present invention which have good stretchability and puncture, the V:Ti ratio should also be from about 0.8:1 to about 1.2:1, preferably about 1:1.
For use in the suspension (slurry) process, the components are employed in quantities which provide an atomic ratio as follows:
Si and/or Al(from the inorganic oxide support):Mg of from about 1:1 to about 50:1, preferably from about 2:1 to about 40:1, more preferably from about 4:1 to about 20:1;
Mg:group IIIA metal of from about 0.01:1 to about 100:1, preferably from about 0.05:1 to about 10:1, more preferably from about 0.1:1 to about 5:1.
Mg:Ti of from about 0.05:1 to about 40:1, preferably from about 0.1:1 to about 20:1, more preferably from about 0.2:1 to about 10:1;
Mg:V, when V is present, of from about 0.05:1 to about 40:1, preferably from about 0.1:1 to about 20:1, more preferably from about 0.2:1 to about 10:1;
V:Ti of from about 0:1 to about 20:1, preferably from about 0:1 to about 10:1, more preferably from about 0:1 to about 3:1.
The compound employed as the liquid medium can be employed in any amount which provides the catalyst component with the desired consistency which does not interfere with the polymerization behavior of the catalyst.
Cocatalyst or Activator
The transition metal catalyst component described above requires a cocatalyst or activator in order to efficiently polymerize the xcex1-olefin monomer(s). Suitable cocatalysts or activator compounds include, for example, Group IIIA metal alkyl, metal alkoxide or metal alkyl halide compounds, particularly C1-C10 alkyl compounds of aluminum. Particularly suitable such compounds include, for example, triethylaluminum, trimethylaluminum, triisobutylaluminum, trihexylaluminum, trioctylaluminum, diethylaluminum chloride, diethylaluminum ethoxide, any combination of any two or more of such compounds and the like.
Also suitable are the aluminoxanes such as those represented by the formula (Al(O)R)x; wherein R is an alkyl group having from 1 to about 8 carbon atoms and x has a value greater than about 4. Particularly suitable aluminoxanes include, for example, methylaluminoxane, hexaisobutyltetraluminoxane, any combination of any two or more of such compounds and the like. Also, mixtures of these aluminoxanes with alkyl aluminum compounds such as, for example, triethylaluminum or tributylaluminum can be employed.
The cocatalyst or activator compound can be employed in the solution process in amounts which provide a ratio of atoms of Group IIIA metal per combined atoms of Ti and V of from about 0.1:1 to about 50:1, preferably from about 1:1 to about 20:1, more preferably from about 2:1 to about 15:1.
The cocatalyst or activator compound can be employed in the suspension (slurry) process in amounts which provide a ratio of atoms of Group IIIA metal per combined atoms of Ti and V of from about 1:1 to about 1000:1, preferably from about 5:1 to about 500:1, more preferably from about 10:1 to about 200:1.
The process of the present invention differs from those of the prior art in that it describes a solution process for controlling the magnitude of the % high density fraction and width of the short chain branching distribution of the ethylene/(xcex1-olefin copolymers of the present invention over a wide range of melt indices and densities and yielding in all resins a narrow molecular weight distribution and small spherulite size. For the copolymers of the present invention the width of the SCBD as observed on an ATEF curve broadens as the magnitude of the % high density fraction of the copolymer increases. In addition, as the magnitude of the % high density fraction of the copolymer increases, the crystallization onset temperature of the resin increases.
According to the current invention a process for controlling the magnitude of the % high density fraction and width of the short chain branching distribution resins is achieved by variation in the catalyst composition prior to the polymerization. This control is independent of support surface area and does not require changes in reactor temperature or deviations from optimum cocatalyst/catalyst ratio ensuring optimum catalyst productivity. The process can be used for preparing as one example cast film resins with improved stretch performance or blown film resins with improved strength properties such as dart impact.
The process of the current invention varies the magnesium:titanium ratio of the silica supported catalyst of the preactivated catalyst prior to polymerization to yield products of a given melt index and density with narrow molecular weight distribution, small spherulite size and the desired magnitude of the % high density fraction and width of the short chain branching distribution. The surprising results of our investigation has demonstrated that in the continuous solution process, for the preparation of a given melt index and density ethylene/xcex1-olefin copolymer, a catalyst with a low magnesium:titanium ratio having a titanium:vanadium molar ratio of 1:1 produces a copolymer with a higher % high density fraction and broader SCBD (as observed from ATREF analysis) than if prepared with a catalysts having a higher magnesium:titanium ratio and a titanium:vanadium molar ratio of 1:1.
The application of this process to resins of various melt index and density allows the product % high density fraction, SCBD, and crystallization temperature to be tailored to the specific product application with resulting improvements in resin physical properties. In the course of this investigation we have also unexpectedly discovered that variations in the catalyst yields resins, which, when made into films, demonstrate improved stretchability and puncture resistance, particularly from narrow molecular weight distribution, broader SCBD LLDPE resins.
This process is conducted at solution conditions described elsewhere in this application.
The copolymers produced by this process are ethylenet/alpha olefin copolymers of the polymerizable comonomers with melt index from 0.2 to 500 (ASTM D 1238, Condition 190xc2x0 C./2.16 kg), preferably from 0.4 to 100 or more preferably from 0.6 to 5 grams/10 minutes; and an I10/I2 from 6.5 to 8.5, preferably from 6.5 to 7.5, more preferably from 6.5 to 7.0, and a density from 0.8 to 0.96 (ASTM D 792), preferably from 0.85 to 0.94, more preferably from 0.90 to 0.93 g/cm3.
Fabricated articles such as molded articles (e.g., injection molded, blow molded, roto molded and compression molded parts) can be made from the copolymers produced by this invention. Of particular utility, however, are films or multilayer film structures from the copolymers of the present invention. The films or film structures can be made using any of the conventional film manufacturing processes. These include blown film, cast film and extrusion coated film processes. Especially preferred are cast films. The copolymers of the present invention can be used alone in the film (i.e., as a monolayer) or they can be used as at least one layer of a multilayer film structure. The films are usually from about 0.4 mils to about 1.2 mils in thickness, preferably about 0.8 mils. Additives can also be included in the copolymers of the present invention for use in the films. For example, additives are often included in copolymers used to make films for pallet wrapping, an especially attractive use area for the copolymers described herein. The skin layer of the pallet wrapping films might contain special additives, e.g., polyisobutylene (PIB), to enhance cling properties of the film to the goods on the pallet.
We have found that specific properties of ethylene/alpha-olefin copolymers which, when made into films for use in pallet wrapping, enhance the ultimate stretchability and puncture properties of the film. High ultimate stretchability is desired to avoid or minimize film breakage, while good puncture properties minimizes film damage. The combination of good stretchabilty and good puncture also leads to good end user economics since less film is used, thereby minimizing waste. The desired ultimate stretchability is at least about 280 percent, while maintaining a puncture of at least about 250 ft-lbs/cm3. Ultimate stretchability is tested by simulated pallet wrapping conditions and is described further in this disclosure. The ethylene/alpha-olefin copolymers used to make pallet wrapping films will have a weight average molecular weight (Mw) to number average molecular weight (Mn) ratio (Mw/Mn) of less than about 3.6, preferably less than about 3.3, more preferably less than about 3.2 and a high density fraction greater than about 17 percent (by weight of the copolymer), preferably at least about 20 percent. The copolymers made using the catalysts and process described in the present invention which have these properties are especially effective in this stretch film application and have not been available here-to-fore. Unblended ethylene/alpha-olefin copolymers having the above specified properties are also within the scope of this invention. The term xe2x80x9cunblendedxe2x80x9d indicates that the copolymers are made within a single reactor system and do not have other polymers blended to them to attain the properties of narrow molecular weight distribution and percent high density fraction, with the exception of additives for other reasons, e.g., PIB for cling enhancement. For this stretch film application, the copolymers preferably have a density from about 0.905 g/cm3 to about 0.935 g/cm3, especially from about 0.912 g/cm3 to about 0.925 g/cm3. The melt index of the copolymers is preferably from about 0.6 grams/10 minutes to about 6 grams/10 minutes, especially from about 1 gram/10 minutes to about 4 grams/10 minutes
Polymerizable Monomers
Suitable polymerizable monomers include, for example xcex1-olefins having from 2 to about 20, preferably from about 2 to about 12, more preferably from about 2 to about 8, carbon atoms and any combination of any two or more of such xcex1-olefins. Particularly suitable such xcex1-olefins include, for example, ethylene, propylene, 1-butene, 1-pentene, 4-methylpentene-1, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-lecene, 1-undecene, 1-dodecene, 1-tridecene, 1-tetradecene, 1-pentadecene, any combination thereof and the like. Preferably, the xcex1-olefins are ethylene, propene, 1-butene, 4-methyl-pentene-1, 1-hexene, 1-octene, and combination of any two or more of such xcex1-olefins.
Polymerization
The catalysts of the present invention can be advantageously employed in the polymerization of monomers by the solution or slurry process.
The slurry process is employed at temperatures of from about 0xc2x0 C. up to a temperature just below the temperature at which the resulting polymer becomes soluble in the inert polymerization medium, preferably at temperatures of from about 60xc2x0 C. to about 105xc2x0 C., more preferably from about 80xc2x0 C. to about 95xc2x0 C.
The solution process is employed at temperatures from the temperature at which the resulting polymer is soluble in the inert reaction medium up to about 275xc2x0 C., preferably at temperatures of from about 145xc2x0 C. to about 260xc2x0 C., more preferably from about 180xc2x0 C. to about 240xc2x0 C.
The polymerization can be employed at pressures of from about 1 to about 2,000, preferably from about 5 to about 500, more preferably from about 10 to about 50, atmospheres.
Molecular weight control agents such as hydrogen can be employed in the manner known to those skilled in the art of polymerizing xcex1-olefins. Usually the greater the amount of hydrogen or terminating agent employed the lower the molecular weight of the resulting polymer. The hydrogen is employed in that quantity which will provide the resulting polymer with the desired molecular weight as indicated by the desired I2 value.
The solution polymerization can be employed in the presence of any suitable inert reaction medium such as, for example, aromatic hydrocarbons, aliphatic hydrocarbons, naphthinic hydrocarbons, combinations thereof and the like. Particularly suitable inert reaction medium include, for example, hexane, heptane, octane, isooctane, nonane, isononane, decane, undecane, dodecane, tridecane, tetradecane, cyclohexane, methylcyclohexane, combinations thereof and the like.
The suspension (slurry) polymerization can be employed in the presence of any suitable inert reaction medium such as, for example, aromatic hydrocarbons, aliphatic hydrocarbons, naphthinic hydrocarbons, liquefied a-olefins, liquefied hydrocarbons, combinations thereof and the like. Particularly suitable inert reaction medium include, for example, isobutane, isopentane, pentane, hexane, heptane, octane, isooctane, nonane, isononane, decane, cyclopentane, cyclohexane, or any combination thereof and the like.